1. Field of the Invention
The present invention relates to a display, and more particularly, to a material for a red organic electroluminescence(EL) device and an organic EL device using the same.
2. Background of the Related Art
As sizes of displays become the larger, demand for a flat display which occupy less spaces increase, as one of which there is the electroluminescence device. There are an inorganic electroluminescence device and an organic electroluminescence device depending on materials used therein. The inorganic electroluminescence device is provided with a light emitting unit to which a high electric field is applied for accelerating electrons, so that the electrons collide onto and excite a luminescent center therein to emit a light. And, the organic electroluminescence device is provided with an electron injection electrode(cathode) and a hole injection electrode(anode) from which electrons and holes are injected into the light emitting unit, so that the injected electrons and the holes are coupled into exciton, to emit a light when the exciton drops from an exited state to a ground state. While the inorganic electroluminescence device that requires a strong electric field due to the above operation principle requires a relatively high driving voltage of approx. 100xcx9c200V, because the organic electroluminescence device has an advantage in that it is operable at a low voltage of 5xcx9c20V, there have been active studies on the organic electroluminescence device. Besides, as the organic electroluminescence device has excellent characteristics, such as a wide angle of view, a fast response speed and a high contrast so on, the organic electroluminescence device can be used as a pixel of a graphic display, or a TV image display or a surface light source, and as the organic electroluminescence device is thin and light and has a good sense of color, the organic electroluminescence device is suitable for a flat display of the next generation.
A structure of a related art organic electroluminescence device will be explained.
The related art organic electroluminescence device is provided with a first electrode formed on a transparent substrate, a hole injection and transport layer formed on the first electrode, a light emitting layer formed on the hole injection and transport layer, an electron injection and transport layer formed on the light emitting layer, and a second electrode formed on the electron injection and transport layer. Considering the operation of electroluminescence devices as consisting of two processes, firstly formation of the exciton(pair of electron-hole) and secondly its decay, the former involves i)carrier injection, ii)carrier transport and iii)carrier recombination, while the latter encompasses a competition between radiative and non-radiative decay channels. Since the disclosure of the organic electroluminescence device by Kodak in 1987, many researchers in the world from Japan, the U. K, and the U.S.A. and etc., participate in the practical application and development of the organic electroluminescence device. Currently, though many studies are underway for materials of the organic EL device, the following materials are in general used as the organic EL device.
The hole transport layer is formed of triphenylamine derivatives, such as N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-(1,1 xe2x80x2-biphenyl)-4,4xe2x80x2-diamine(TPD) or N,Nxe2x80x2-dinaphthyl-N,Nxe2x80x2-phenyl-(1,1xe2x80x2-biphenyl)-4,4xe2x80x2-diamine(NPD). And, the electron transport layer is in general formed of alkyl metal complex, such as tris(8-hydroxy quinolate) aluminum(Alq3). The organic light emitting layer is formed of Alq3 as base with dopant of organic EL dyes for adjusting color of lights. In the meantime, a red EL device, a green EL device and a blue EL device are required for realization of a full color display, wherein coumarine 6 or quinacridone derivatives are used as dopants in a case of the green EL device, and DCM(4-dicyanomethylene-2-p-dimethylaminostyryl-6-methyl-4H-pyran) derivatives are used as dopants in a case of the red EL device.
However, the related art organic EL device has the following problems.
It is known that a stability of the green EL device has reached to a practicable level. However, in the cases of the blue EL device and the red EL device, colors of emitted lights and stabilities are not reached to practicable levels and luminance efficiencies are also not reached to a satisfactory level.
Accordingly, the present invention is directed to a material for a red organic EL device and an organic EL device using the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a material for a red organic EL device and an organic EL device using the same, which can improve an luminance efficiency, an emitting light color and a device stability.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided the compound of the following structural formula: 
1) Wherein G1 and G2 are identical or different electron withdrawing groups except a case when both of G1 and G2 are cyano groups, or G1 and G2 are electron withdrawing groups interconnected with a molecular chain to form a cyclic compound or a heterocyclic compound;
2) And, wherein the R1 or the R2 is any one selected from a substituted or unsubstituted alkyl group (with 1xcx9c5 carbons), a substituted or unsubstituted aryl group and xe2x80x94CHxe2x95x90CHxe2x80x94A1, the chemical formula A1 being a 4-dialklyamino-phenyl, a 4-dialkylamino-2-alkoxyphenyl, a julolidine, an 8-alkoxy julolidine, a diphenylaminophenyl, a diphenylaminophenyl having an alkyl group substituted therein, or a diphenylaminophenyl having an alkoxy group substituted therein where the alkyl or the alkoxy has 1xcx9c5 carbons;
3) And, wherein X is O, N, Se or S.
In another aspect of the present invention, there is provided an organic electroluminescence device having a first electrode, a second electrode and a stack of a plurality of organic layers, including a light emitting layer of a compound with the aforementioned structural formula.
In further aspect of the present invention, there is provided an organic electroluminescence device having a first electrode, a second electrode and a stack of a plurality of organic layers, including a light emitting layer doped with a compound with the aforementioned structural formula.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.